That may be the biggest bunch of nothing I've ever tried to read in my life...
I wouldn't even know where to start to point out your fantasized misconceptions in the above....
Then find a place. Your post, frankly, was rude, added nothing constructive to the thread, and failed to specify any errors in mine or points in which mine did not reference the issue you raised.
Sorry if you had difficulty reading my post; I'll try to boil it down for you.
1. You said you wanted a flip phone. Flip phones are comprised of two parts: the main body, and the display. The battery by conventional design can only be housed in one part, the body. That means a greater limitation to the size of the battery as a % of the volume of the entire phone when compared to a bar style phone.
2. You said you wanted a more durable phone. Flip phones have categorically been less durable than bar phones.
3. You said a sufficient battery could fit in a flip phone and still be notably smaller. Battery requirements to drive a wifi hotspot are substantially higher than those required by normal phone data usage. "Large" phones now, which have substantially larger capacity batteries than would fit in a smaller flip phone, already have a pretty limited duration for which they can operate as a hot spot (especially if running on LTE), meaning that while a company could make a compact flip phone that had the capability, it would not have the utility to make it worthwhile for enough people to warrant its inclusion from a cost perspective, as the company still has to pass along that cost to the majority who would not be interested in the feature given that limitation.
You asked "why not" in your response, and I gave reasons. I've summed them up here again in the hope you'll be able to see my reasoning. If you don't like someone's response when you open up a conversation, try to be civil and provide counterpoints. If I mistook your initial question (though that seems unlikely from your initial response), that's fine - say so and provide clarification.
That said, I too would love the option of a small flip phone that could effectively do all these things, be more durable and compact, etc, but the reasons above are "why not."
And once again, let's try to keep this friendly. These forums should not be the place for malignant posts.